Playlists for real-time or near real-time streaming

ABSTRACT

Methods, systems and machine readable storage medium for allowing playback of streaming media at playback rates of other than 1× are described. In one embodiment, a method can determine different sets of I-frames that are available before a display deadline, where each set can have a different cadence, and one of the sets can be selected for download and display to achieve playback at other than 1×. Byte range requests from a client device can be used to retrieve each of the I-frames. Other methods, system and media are also described.

RELATED APPLICATIONS

This application claims the benefit of the filing date, under 35 U.S.C. §119(e), of U.S. Provisional Application No. 61/493,329 filed on Jun. 3, 2011. The present U.S. patent application is also related to the following U.S. patent applications, each of which is incorporated herein by reference:

(1) application Ser. No. 12/479,690 (Docket No. P7437US1), filed Jun. 5, 2009, entitled “REAL-TIME OR NEAR REAL-TIME STREAMING;”

(2) application Ser. No. 12/479,698 (Docket No. P7437US2), filed Jun. 5, 2009, entitled “VARIANT STREAMS FOR REAL-TIME OR NEAR REAL-TIME STREAMING;”

(3) application Ser. No. 12/479,732 (Docket No. P7437US3), filed Jun. 5, 2009, entitled “UPDATABLE REAL-TIME OR NEAR REAL-TIME STREAMING,” and

(4) application Ser. No. 12/479,735 (Docket No. P7437US4), filed Jun. 5, 2009, entitled “PLAYLISTS FOR REAL-TIME OR NEAR REAL-TIME STREAMING.”

TECHNICAL FIELD

Embodiments of the invention relate to data transmission techniques. More particularly, embodiments of the invention relate to techniques that allow streaming of data using non-streaming protocols such as, for example, HyperText Transfer Protocol (HTTP).

BACKGROUND

Streaming of content generally refers to multimedia content that is constantly transmitted from a server device and received by a client device. The content is usually presented to an end-user while it is being delivered by the streaming server. The name refers to the delivery method of the medium rather than to the medium itself.

Current streaming services generally require specialized servers to distribute “live” content to end users. In any large scale deployment, this can lead to great cost, and requires specialized skills to set up and run. This results in a less than desirable library of content available for streaming.

SUMMARY OF THE DESCRIPTION

A method in one embodiment can use byte range request parameters that are specified in a tag associated with a URL that conforms to the HTTP live streaming protocol (see http://tools.ietf.org/html/draft-pantos-http-live-streaming-06) in order to retrieve streaming content from a file that is stored by a server. A client system receives a playlist containing URLs and associated tags specifying portions of a program that can be streamed according to this protocol, and those tags include byte range parameters (e.g., length of the range and offset from a position in the file); the URLs are transmitted from the client to the server which uses the byte range parameters to retrieve and transmit the portion of the program. In this way, the media content can be stored as a single large file rather than multiple smaller files and portions of the content can be retrieved through the HTTP live streaming protocol by using the byte range requests and then presented in a 1× playback mode by a player at a client.

A method to provide “trick play” mode playback (e.g. fast forward or rewind) for streaming media (e.g., a movie) delivered through an HTTP streaming protocol is also described. The method uses an I-frame playlist that includes URLs which refer to I-frames (which are keyframes or intra-coded frames that can be decoded independently of other video frames). A player device or client can download and use a standard playlist which includes URLs that refer to all of the content and allows playback at a normal (e.g. 1×) rate, and the player device or client can download and use the I-frame playlist that includes URLs for I-frames for playback at other than the normal rate (e.g. 8× or 8 times faster than the normal playback rate). The I-frame playlist can include byte range parameters, as part of the parameters associated with URLs in the playlist, that specify a range of data in a file that is data for a particular I-frame of video data; the range can be specified by a length of data (in, e.g., bytes) and a starting position in the file such as an offset from the beginning of the file. In this way, the I-frame playlist can include those parameters specifying byte ranges within a file on a server that refer to only I-frames in order to present a playback in a trick mode on the client device. The client device can resume a normal playback by using the standard playlist file which contains URLs to the same file that includes the I-frames retrieved when the I-frame playlist is used to provide trick play of the streaming media. In one embodiment (e.g. MPEG-DASH playlist files), the standard playlist file that is used for 1× playlist also includes data specifying Iframe locations. In one embodiment, a tag in an I-frame playlist can include a parameter that refers to the span of time between a current I-frame and the next I-frame, and this span of time can be used to determine which I-frames to use for a given rate (e.g. 8× or 16×) of playback. In addition, in one embodiment, a client device can use a variant playlist that refers to at least one standard playlist (at 1×) for a program (e.g., a movie) and an I-frame playlist for trick play mode for the same program.

The phrase “byte range” will be understood to include a range specified by a number of bytes or a number of other sizes or groups of data. A byte can be, for example, 8 bits of 9 bits or 16 bits or 32 bits or 36 bits.

A method, in one embodiment, to provide “trick play” mode playback of streaming media can receive a first playlist that includes a URL for a second playlist and a URL for a third playlist; the second playlist can include a plurality of URLs and associated tags specifying portions (for example, portions specified in a byte range) of a file containing Iframes, and the third playlist can include a plurality of URLs (or a single URL) to display a video at a 1× playback speed. The first playlist can be a variant playlist which includes a plurality of URLs for 1× playback (and each of these URLs provide different resolutions (e.g. 640 pixels by 480 pixels, etc.) or qualities (e.g. color bit depth)) and a plurality of URLs for Iframe only playlists (and each of these URLs for Iframe playlists provide different resolutions or qualities for trick play mode playback at other than 1×). The tags associated with the plurality of URLs in the third playlist can also include byte ranges which each specify a range of data for retrieval of content and playback of the content at the 1× playback rate. The method can also include (a) determining a playback speed which is other than 1× (such as 8× or 16× or 32× for fast forward or −8× or −16× or −32× for rewind) and (b) transmitting the URL for the second playlist in response to determining the playback speed, (c) receiving the second playlist, (d) transmitting requests for Iframes using URLs and associated tags in the second playlist, and (e) presenting (e.g., displaying on a display device) the Iframes, at the selected playback speed, that are received in response to requests for Iframes.

In an embodiment, a method of the invention can use a cadence based selection of Iframes to select a subset of available Iframes so that the Iframes that are downloaded and displayed are at least somewhat evenly distributed in time; further, the method can limit the subset to a number which is less than the total number of available Iframes. This method can include (a) determining a set of parameters, such as a playback rate and a period of time that is available to download at least one Iframe, (b) determining a first set of available Iframes, wherein the first set is determined based on the parameters which can dynamically change over time, (c) determining a plurality of subsets of Iframes, wherein each of the plurality of subsets is a subset of the Iframes in the first set, (d) determining an estimated download time for each of the plurality of subsets of Iframes, (e) selecting one of the plurality of subsets of Iframes based upon the estimated download times and the set of parameters, and (f) receiving and displaying Iframes in the selected one of the plurality of subsets of Iframes. In one embodiment of this method, the displaying of Iframes provides a trick play playback mode, at the playback rate, of video content in the Iframes, and each Iframe can be retrieved (e.g. downloaded) using a URL and an associated tag that includes a byte range identifying a portion of a file containing the corresponding Iframe. The set of parameters can include a display deadline parameter and a current movie time of a current Iframe being displayed; the period of time that is available to download at least one Iframe can be derived from the current movie time and the playback rate and the display deadline parameter which can be set as a fixed duration of time (e.g. ½ second or 1 second or 2 seconds). In one embodiment, the display deadline parameter (e.g., 1 second) is multiplied by the playback rate to produce a product (e.g. 1× (8×)), which is a time value, that is added to the current movie time to derive the period of time that is available to download at least one Iframe. In one embodiment, the period of time available to download at least one Iframe is simply the time from now to the display deadline time. The use of a display deadline can ensure that the user will see at least one Iframe per deadline period (e.g., at least one Iframe per second). In one embodiment, each of the subsets of Iframes has a predetermined cadence which is distinct among the subsets of Iframes such that each of the subsets has a different cadence relative to the other subsets' cadences. In one embodiment, the predetermined cadence of each of the plurality of subsets of Iframes is one of: (a) every one of the available Iframes in the first set; (b) every other one of the available Iframes; (c) every third one of the available Iframes, and so on. In one embodiment, the set of parameters includes a limit on the number of Iframes in each of the subsets such that no subset can have more Iframes than a predetermined number.

Other methods are described, and systems and machine readable non-transitory storage media are also described.

The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, and also those disclosed in the Detailed Description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements.

FIG. 1 is a block diagram of one embodiment of a server and clients that can send and receive real-time, or near real-time, content.

FIG. 2A is a flow diagram of one embodiment of a technique for one or more server devices to support media content using non-streaming protocols.

FIG. 2B is a flow diagram of one embodiment of a technique for one or more server devices to provide dynamically updated playlists to one or more client devices.

FIG. 2C is a flow diagram of one embodiment of a technique for one or more server devices to provide media content to client devices using multiple bit rates.

FIG. 3A is a flow diagram of one embodiment of a technique for a client device to support streaming of content using non-streaming protocols.

FIG. 3B is a flow diagram of one embodiment of a technique for a client device to support streaming of content using multiple bit rates.

FIG. 4 is a block diagram of one embodiment of a server stream agent.

FIG. 5 is a block diagram of one embodiment of a client stream agent.

FIG. 6 illustrates on embodiment, of a playlist file with multiple tags.

FIG. 7 is a flow diagram of one embodiment of a playback technique for assembled streams as described herein.

FIG. 8 is a block diagram of one embodiment of an electronic system.

FIG. 9A is a flowchart showing an example of how a client device can switch between alternative content in a variant playlist.

FIG. 9B is a further flowchart showing how a client device can switch between content in two playlists.

FIG. 9C is a further flowchart showing an example of how a client device can switch between content using audio pattern matching.

FIG. 9D shows diagrammatically how the method of FIG. 9C is implemented with audio pattern matching.

FIG. 10 shows an example of a variant playlist that contains a plurality of URLs for playback at 1× (normal speed), each of these URLs providing a playlist for 1× playback at different resolutions or qualities, and the variant playlist also includes a plurality of URLs for playback at rates other than 1×.

FIG. 11 illustrates a method, which can be performed at a server, for creating Iframe playlists.

FIG. 12 is a block diagram representation of a client device which can be used to process the Iframe playlists and can perform the methods shown in FIG. 14 or 15.

FIG. 13A shows an example of a video file, such as a movie or video on demand, with the Iframes in the video file.

FIG. 13B shows an example of an Iframe playlist for the video file shown in FIG. 13A.

FIG. 14 is a flowchart showing an example of a method for processing an Iframe playlist.

FIG. 15 is a flowchart showing an example of another method for processing an Iframe playlist.

FIG. 16 shows an example of a video file having Iframes and how a limit can be used to exclude cadences that exceed the limit of Iframes.

FIGS. 17A, 17B, 17C, and 17D show examples of different cadences which represent different subsets of the available Iframes.

FIG. 18 is a flowchart showing a method of switching between Iframe playlists of different resolution and/or quality.

FIG. 19 illustrates a block diagram of an exemplary API architecture usable in some embodiments of the invention.

FIG. 20 shows an exemplary embodiment of a software stack usable in some embodiments of the invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth. However, embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description.

The present description includes material protected by copyrights, such as illustrations of graphical user interface images. The owners of the copyrights, including the assignee of the present invention, hereby reserve their rights, including copyright, in these materials. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office file or records, but otherwise reserves all copyrights whatsoever. Copyright Apple Inc. 2009.

One aspect of this description relates to the use of byte range requests in playlists that are described herein, and another aspect of this description relates to methods of providing fast forward or rewind (reverse) playback from Iframes in the streaming media and the use of playlists with timing information that allows a cadence of Iframes to be selected when providing fast forward or rewind. These aspects will be described in conjunction with FIGS. 10-18 after providing background information in conjunction with FIGS. 1-9D.

In one embodiment, techniques and components described herein can include mechanisms to deliver streaming experience using non-streaming protocols (e.g., HTTP) and other technologies (e.g., Motion Picture Expert Group (MPEG) streams). For example, near real-time streaming experience can be provided using HTTP to broadcast a “live” musical or sporting event, live news, a Web camera feed, etc. In one embodiment, a protocol can segment incoming media data into multiple media files and store those segmented media files on a server. The protocol can also build a playlist file that includes Uniform Resource Identifiers (URIs) that direct the client to the segmented media files stored on a server. When the segmented media files are played back in accordance with the playlist file(s), the client can provide the user with a near real-time broadcast of a “live” event. Pre-recorded content can be provided in a similar manner.

In one embodiment, the server can dynamically introduce supplementary or alternative media content (e.g., advertisements, statistics related to a sporting event, additional media content to the main presentation) into the broadcast event. For example, during client playback of a media event, the server can add additional URIs to the playlist file, the URIs may identify a location from which a client can download a supplementary media file. The client can be instructed to periodically retrieve from the server one or more updated playlist file(s) in order to access any supplementary or additional (or both) media content the server has introduced.

In one embodiment, the server can operate in either cumulative mode or in rolling mode. In cumulative mode, the server can create a playlist file and append media file identifiers to the end of the playlist file. The client then has access to all parts of the stream from a single playlist file (e.g., a user can start at the middle of a show) when downloaded. In rolling mode, the server may limit the availability of media files by removing media file identifiers from the beginning of the playlist file on a rolling basis, thereby providing a sliding window of media content accessible to a client device. The server can also add media file identifiers to the playlist and, in rolling mode, the server can limit the availability of media files to those that have been most recently added to the playlist. The client then repeatedly downloads updated copies of the playlist file to continue viewing. The rolling basis for playlist downloading can be useful when the content is potentially unbounded in time (e.g. content from a continuously operated web cam). The client can continue to repeatedly request the playlist in the rolling mode until it finds an end tag in the playlist.

In one embodiment, the mechanism supports bit rate switching by providing variant streams of the same presentation. For example, several versions of a presentation to be served can be stored on the server. Each version can have substantially the same content but be encoded at different bit rates. This can allow the client device to switch between bit rates depending on, for example, a detection of the available bandwidth, without compromising continuity of playback.

In one embodiment, protection features may be provided to protect content against unauthorized use. For example, non-sequential media file numbering may be used to prevent prediction. Encryption of media files may be used. Partial media file lists may be used. Additional and/or different protection features may also be provided.

FIG. 1 is a block diagram of one embodiment of a server and clients that can send and receive real-time, or near real-time, content. The example of FIG. 1 provides a simple server-client connection with two clients coupled with a server via a network. Any number of clients may be supported utilizing the techniques and mechanisms described herein. Further, multiple servers may provide content and/or may operate together to provide content according to the techniques and mechanisms described herein. For example, one server may create the content, create the playlists and create the multiple media (e.g. files) and other servers store and transmit the created content.

Network 110 may be any type of network whether wired, wireless (e.g., IEEE 802.11, 802.16) or any combination thereof. For example, Network 100 may be the Internet or an intranet. As another example, network 110 may be a cellular network (e.g., 3G, CDMA). In one embodiment, client devices 150 and 180 may be capable of communicating over multiple network types (e.g. each device can communicate over a WiFi wireless LAN and also over a wireless cellular telephone network). For example, client devices 150 and 180 may be smart phones or cellular-enabled personal digital assistants that can communicate over cellular radiotelephone networks as well as data networks. These devices may be able to utilize the streaming mechanisms described herein over either type of network or even switch between networks as necessary.

Server 120 may operate as a HTTP server in any manner known in the art. That is server 120 includes a HTTP server agent 145 that provides content using HTTP protocols. While the example of FIG. 1 is described in terms of HTTP, other protocols can be utilized in a similar manner. Segmenter 130 and indexer 135 are agents that reside on server 120 (or multiple servers) to provide content in media files with a playlist file as described herein. These media files and playlist files may be provided over network 110 via HTTP server agent 145 (or via other servers) using HTTP protocols. Agents as discussed herein can be implemented as hardware, software, firmware or a combination thereof.

Segmenter 130 may function to divide the stream of media data into multiple media files that may be transmitted via HTTP protocols. Indexer 135 may function to create a playlist file corresponding to the segmented media files so that client devices can reassemble the media files to provide real-time, or near real-time, transmission of the content provided by server 120. In response to one or more requests from a client device, HTTP server agent 145 (or other servers) may transmit one or more playlist files as generated by indexer 135 and media files of content as generated by segmenter 130. Server 120 may further include optional security agent 140 that provides one or more of the security functions (e.g. encryption) discussed herein. Server 120 may also include additional components not illustrated in FIG. 1.

Client devices 150 and 180 may receive the playlist files and media files from server 120 over network 110. Client devices may be any type of electronic device that is capable of receiving data transmitted over a network and generate output utilizing the data received via the network, for example, wireless mobile devices, PDAs, entertainment devices, consumer electronic devices, etc. The output may be any media type of combination of media types, including, for example, audio, video or any combination thereof.

Client device 150 can include assembler agent 160 and output generator agent 165. Similarly, client device 180 can include assembler agent 190 and output generator agent 195. Assembler agents 160 and 180 receive the playlist files from server 120 and use the playlist files to access and download media files from server 120. Output generator agents 165 and 195 use the downloaded media files to generate output from client devices 150 and 160, respectively. The output may be provided by one or more speakers, one or more display screens, a combination of speakers and display screens or any other input or output device. The client devices can also include memory (e.g. flash memory or DRAM, etc.) to act as a buffer to store the media files (e.g. compressed media files or decompressed media files) as they are received; the buffer can provide many seconds worth of presentable content beyond the time of content currently being presented so that the buffered content can later be displayed while new content is being downloaded. This buffer can provide presentable content while the client device is attempting to retrieve content through an intermittently slow network connection and hence the buffer can hide network latency or connection problems.

Client devices 150 and 180 may further include optional security agents 170 and 185, respectively that provide one or more of the security functions discussed herein. Client devices 150 and 180 may also include additional components not illustrated in FIG. 1.

In one embodiment, the techniques that are described in this application may be used to transmit an unbounded stream of multimedia data over a non-streaming protocol (e.g., HTTP). Embodiments can also include encryption of media data and/or provision of alternate versions of a stream (e.g., to provide alternate bit rates). Because media data can be transmitted soon after creation, the data can be received in near real-time. Example data formats for files as well as actions to be taken by a server (sender) and a client (receiver) of the stream of multimedia data are provided; however, other formats can also be supported.

A media presentation that can be transmitted as a simulated real-time stream (or near real-time stream) is specified by a Universal Resource Indicator (URI) that indicates a playlist file. In one embodiment, the playlist file is an ordered list of additional URIs. Each URI in the playlist file refers to a media file that is a segment of a stream, which may be a single contiguous stream of media data for a particular program.

In order to play the stream of media data, the client device obtains the playlist file from the server. The client also obtains and plays each media data file indicated by the playlist file. In one embodiment, the client can dynamically or repeatedly reload the playlist file to discover additional and/or different media segments.

The playlist files may be, for example, Extended M3U Playlist files. In one embodiment, additional tags that effectively extend the M3U format are used. M3U refers to Moving Picture Experts Group Audio Layer 3 Uniform Resource Locator (MP3 URL) and is a format used to store multimedia playlists. A M3U file is a text file that contains the locations of one or more media files for a media player to play.

The playlist file, in one embodiment, is an Extended M3U-formatted text file that consists of individual lines. The lines can be terminated by either a single LF character or a CR character followed by a LF character. Each line can be a URI, a blank line, or start with a comment character (e.g. ‘#’). URIs identify media files to be played. Blank lines can be ignored.

Lines that start with the comment character can be either comments or tags. Tags can begin with #EXT, while comment lines can begin with #. Comment lines are normally ignored by the server and client. In one embodiment, playlist files are encoded in UTF-8 format. UTF-8 (8-bit Unicode Transformation Format) is a variable-length character encoding format. In alternate embodiments, other character encoding formats can be used.

In the examples that follow, an Extended M3U format is utilized that includes two tags: EXTM3U and EXTINF. An Extended M3U file may be distinguished from a basic M3U file by a first line that includes “#EXTM3U”.

EXTINF is a record marker that describes the media file identified by the URI that follows the tag. In one embodiment, each media file URI is preceded by an EXTINF tag, for example:

#EXTINF: <duration>,<title>

where “duration” specifies the duration of the media file and “title” is the title of the target media file.

In one embodiment, the following tags may be used to manage the transfer and playback of media files:

EXT-X-TARGETDURATION EXT-X-MEDIA-SEQUENCE EXT-X-KEY EXT-X-PROGRAM-DATE-TIME EXT-X-ALLOW-CACHE EXT-X-STREAM-INF EXT-X-ENDLIST These tags will each be described in greater detail below. While specific formats and attributes are described with respect to each new tag, alternative embodiments can also be supported with different attributes, names, formats, etc.

The EXT-X-TARGETDURATION tag can indicate the approximate duration of the next media file that will be added to the presentation. It can be included in the playback file and the format can be:

-   -   #EXT-X-TARGETDURATION:<seconds>         where “seconds” indicates the duration of the media file. In one         embodiment, the actual duration may differ slightly from the         target duration indicated by the tag. In one embodiment, every         URI indicating a segment will be associated with an approximate         duration of the segment; for example, the URI for a segment may         be prefixed with a tag indicating the approximate duration of         that segment.

Each media file URI in a playlist file can have a unique sequence number. The sequence number, if present, of a URI is equal to the sequence number of the URI that preceded it, plus one in one embodiment. The EXT-X-MEDIA-SEQUENCE tag can indicate the sequence number of the first URI that appears in a playlist file and the format can be:

-   -   #EXT-X-MEDIA-SEQUENCE:<number>         where “number” is the sequence number of the URI. If the         playlist file does not include a #EXT-X-MEDIA-SEQUENCE tag, the         sequence number of the first URI in the playlist can be         considered 1. In one embodiment, the sequence numbering can be         non-sequential; for example, non-sequential sequence numbering         such as 1, 5, 7, 17, etc. can make it difficult to predict the         next number in a sequence and this can help to protect the         content from pirating. Another option to help protect the         content is to reveal only parts of a playlist at any given time.

Some media files may be encrypted. The EXT-X-KEY tag provides information that can be used to decrypt media files that follow it and the format can be:

-   -   #EXT-X-KEY:METHOD=<method>[,URI=“<URI>”]         The METHOD parameter specifies the encryption method and the URI         parameter, if present, specifies how to obtain the key.

An encryption method of NONE indicates no encryption. Various encryption methods may be used, for example AES-128, which indicates encryption using the Advance Encryption Standard encryption with a 128-bit key and PKCS7 padding [see RFC3852]. A new EXT-X-KEY tag supersedes any prior EXT-X-KEY tags.

An EXT-X-KEY tag with a URI parameter identifies the key file. A key file may contain the cipher key that is to be used to decrypt subsequent media files listed in the playlist file. For example, the AES-128 encryption method uses 16-octet keys. The format of the key file can be a packed array of 16 octets in binary format.

Use of AES-128 normally requires that the same 16-octet initialization vector (IV) be supplied when encrypting and decrypting. Varying the IV can be used to increase the strength of the cipher. When using AES-128 encryption, the sequence number of the media file can be used as the IV when encrypting or decrypting media files.

The EXT-X-PROGRAM-DATE-TIME tag can associate the beginning of the next media file with an absolute date and/or time and can include or indicate a time zone. In one embodiment, the date/time representation is ISO/IEC 8601:2004. The tag format can be:

-   -   EXT-X-PROGRAM-DATE-TLME:<YYYY-MM-DDThh:mm:ssZ>

The EXT-X-ALLOW-CACHE tag can be used to indicate whether the client may cache the downloaded media files for later playback. The tag format can be:

-   -   EXT-X-ALLOW-CACHE:<YES|NO>

The EXT-X-ENDLIST tag indicates in one embodiment that no more media files will be added to the playlist file. The tag format can be:

-   -   EXT-X-ENDLIST         In one embodiment, if a playlist contains the final segment or         media file then the playlist will have the EXT-X-ENDLIST tag.

The EXT-X-STREAM-INF tag can be used to indicate that the next URI in the playlist file identifies another playlist file. The tag format can be, in one embodiment:

-   -   EXT-X-STREAM-INF:[attribute=value][,attribute=value]*<URI>         where the following attributes may be used. The attribute         BANDWIDTH=<n> is an approximate upper bound of the stream bit         rate expressed as a number of bits per second. The attribute         PROGRAM-ID=<i> is a number that uniquely identifies a particular         presentation within the scope of the playlist file. A playlist         file may include multiple EXT-X-STREAM-INF URIs with the same         PROGRAM-ID to describe variant streams of the same presentation.         Variant streams and variant playlists are described further in         this disclosure (e.g. see FIGS. 9A-9D).

The foregoing tags and attributes can be used by the server device to organize, transmit and process the media files that represent the original media content. The client devices use this information to reassemble and present the media files in a manner to provide a real-time, or near real-time, streaming experience (e.g. viewing of a live broadcast such as a music or sporting event) to a user of the client device.

Each media file URI in a playlist file identifies a media file that is a segment of the original presentation (i.e., original media content). In one embodiment, each media file is formatted as a MPEG-2 transport stream, a MPEG-2 program stream, or a MPEG-2 audio elementary stream. The format can be specified by specifying a CODEC, and the playlist can specify a format by specifying a CODEC. In one embodiment, all media files in a presentation have the same format; however, multiple formats may be supported in other embodiments. A transport stream file should, in one embodiment, contain a single MPEG-2 program, and there should be a Program Association Table and a Program Map Table at the start of each file. A file that contains video SHOULD have at least one key frame and enough information to completely initialize a video decoder. Clients SHOULD be prepared to handle multiple tracks of a particular type (e.g. audio or video) by choosing a reasonable subset. Clients should, in one embodiment, ignore private streams inside Transport Streams that they do not recognize. The encoding parameters for samples within a stream inside a media file and between corresponding streams across multiple media files SHOULD remain consistent. However clients SHOULD deal with encoding changes as they are encountered, for example by scaling video content to accommodate a resolution change.

FIG. 2A is a flow diagram of one embodiment of a technique for one or more server devices to support media content using non-streaming protocols. The example of FIG. 2A is provided in terms of HTTP; however, other non-streaming protocols can be utilized in a similar manner. The example of FIG. 2A is provided in terms of a single server performing certain tasks. However, any number of servers may be utilized. For example, the server that provides media files to client devices may be a different device than a server that segments the content into multiple media files.

The server device receives content to be provided in operation 200. The content may represent live audio and/or video (e.g., a sporting event, live news, a Web camera feed). The content may also represent pre-recorded content (e.g., a concert that has been recorded, a training seminar, etc.). The content may be received by the server according to any format and protocol known in the art, whether streamed or not. In one embodiment, the content is received by the server in the form of a MPEG-2 stream; however, other formats can also be supported.

The server may then store temporarily at least portions of the content in operation 210. The content or at least portions of the content may be stored temporarily, for example, on a storage device (e.g., hard disk in a Storage Area Network, etc.) or in memory. Alternatively, the content may be received as via a storage medium (e.g., compact disc, flash drive) from which the content may be transferred to a storage device or memory. In one embodiment, the server has an encoder that converts, if necessary, the content to one or more streams (e.g., MPEG-2). This conversion can occur without storing permanently the received content, and in some embodiments, the storage operation 210 may be omitted or it may be a longer term storage (e.g. an archival storage) in other embodiments.

The content to be provided is segmented into multiple media files in operation 220. In one embodiment, the server converts a stream into separate and distinct media files (i.e., segments) that can be distributed using a standard web server. In one embodiment, the server segments the media stream at points that support effective decode of the individual media files (e.g., on packet and key frame boundaries such as PES packet boundaries and i-frame boundaries). The media files can be portions of the original stream with approximately equal duration. The server also creates a URI for each media file. These URIs allow client devices to access the media files.

Because the segments are served using HTTP servers, which inherently deliver whole files, the server should have a complete segmented media file available before it can be served to the clients. Thus, the client may lag (in time) the broadcast by at least one media file length. In one embodiment, media file size is based on a balance between lag time and having too many files.

In one embodiment, two session types (live session and event session) are supported. For a live session, only a fixed size portion of the stream is preserved. In one embodiment, content media files that are out of date are removed from the program playlist file, and can be removed from the server. The second type of session is an event session, where the client can tune into any point of the broadcast (e.g., start from the beginning, start from a mid-point). This type of session can be used for rebroadcast, for example.

The media files are stored in the server memory in operation 230. The media files can be protected by a security feature, such as encryption, before storing the files in operation 230. The media files are stored as files that are ready to transmit using the network protocol (e.g., HTTP or HTTPS) supported by the Web server application on the server device (or supported by another device which does the transmission).

One or more playlist files are generated to indicate the order in which the media files should be assembled to recreate the original content in operation 240. The playlist file(s) can utilize Extended M3U tags and the tags described herein to provide information for a client device to access and reassemble the media files to provide a streaming experience on the client device. A URI for each media file is included in the playlist file(s) in the order in which the media files are to be played. The server can also create one or more URIs for the playlist file(s) to allow the client devices to access the playlist file(s).

The playlist file(s) can be stored on the server in operation 250. While the creation and storing of media files and playlist file(s) are presented in a particular order in FIG. 2A, a different order may also be used. For example, the playlist file(s) may be created before the media files are created or stored. As another example, the playlist file(s) and media files may be created before either are stored.

If media files are to be encrypted the playlist file(s) can define a URI that allows authorized client devices to obtain a key file containing an encryption key to decrypt the media files. An encryption key can be transmitted using a secure connection (e.g., HTTPS). As another example, the playlist file(s) may be transmitted using HTTPS. As a further example, media files may be arranged in an unpredictable order so that the client cannot recreate the stream without the playlist file(s).

If the encryption method is AES-128, AES-128 CBC encryption, for example, may be applied to individual media files. In one embodiment, the entire file is encrypted. Cipher block chaining is normally not applied across media files in one embodiment. The sequence of the media files is use as the IV as described above. In one embodiment, the server adds an EXT-X-KEY tag with the key URI to the end of the playlist file. The server then encrypts all subsequent media files with that key until a change in encryption configuration is made.

To switch to a new encryption key, the server can make the new key available via a new URI that is distinct from all previous key URIs used in the presentation. The server also adds an EXT-X-KEY tag with the new'key URI to the end of a playlist file and encrypts all subsequent media files with the new key.

To end encryption, the server can add an EXT-X-KEY tag with the encryption method NONE at the end of the playlist file. The tag (with “NONE” as the method) does not include a URI parameter in one embodiment. All subsequent media files are not encrypted until a change in encryption configuration is made as described above. The server does not remove an EXT-X-KEY tag from a playlist file if the playlist file contains a URI to a media file encrypted with that key. The server can transmit the playlist file(s) and the media files over the network in response to client requests in operation 270, as described in more detail with respect to FIG. 3A.

In one embodiment, a server transmits the playlist file to a client device in response to receiving a request from a client device for a playlist file. The client device may access/request the playlist file using a URI that has been provided to the client device. The URI indicates the location of the playlist file on the server. In response, the server may provide the playlist file to the client device. The client device may the utilize tags and URIs (or other identifiers) in the playlist file to access the multiple media files.

In one embodiment, the server may limit the availability of media files to those that have been most recently added to the playlist file(s). To do this, each playlist file can include only one EXT-X-MEDIA-SEQUENCE tag and the value can be incremented by one for every media file URI that is removed from the playlist file. Media file URIs can be removed from the playlist file(s) in the order in which they were added. In one embodiment, when the server removes a media file URI from the playlist file(s) the media file remains available to clients for a period of time equal to the duration of the media file plus the duration of the longest playlist file in which the media file has appeared.

The duration of a playlist file is the sum of the durations of the media files within that playlist file. Other durations can also be used. In one embodiment, the server can maintain at least three main presentation media files in the playlist at all times unless the EXT-X-ENDLIST tag is present.

FIG. 2B is a flow diagram of one embodiment of a technique for one or more server devices to provide dynamically updated playlists to one or more client devices. The playlists can be updated using either of the cumulative mode or the rolling mode described herein. The example of FIG. 2B is provided in terms of HTTP; however, other non-streaming protocols (e.g. HTTPS, etc.) can be utilized in a similar manner. The example of FIG. 2B is provided in terms of a server performing certain tasks. However, any number of servers may be utilized. For example, the server that provides media files to client devices may be a different device than the server that segments the content into multiple media files.

The server device receives content to be provided in operation 205. The server may then temporarily store at least portions of the content in operation 215. Operation 215 can be similar to operation 210 in FIG. 2A. The content to be provided is segmented into multiple media files in operation 225. The media files can be stored in the server memory in operation 235. The media files can be protected by a security feature, such as encryption, before storing the files in operation 235.

One or more playlist files are generated to indicate the order in which the media files should be assembled to recreate the original content in operation 245. The playlist file(s) can be stored on the server in operation 255. While the creation and storing of media files and playlist file(s) are presented in a particular order in FIG. 2B, a different order may also be used.

The server (or another server) can transmit the playlist file(s) and the media files over the network in response to client requests in operation 275, as described in more detail with respect to FIGS. 3A-3B.

The playlist file(s) may be updated by a server for various reasons. The server may receive additional data to be provided to the client devices in operation 285. The additional data can be received after the playlist file(s) are stored in operation 255. The additional data may be, for example, additional portions of a live presentation, or additional information for an existing presentation. Additional data may include advertisements or statistics (e.g. scores or data relating to a sporting event). The additional data could be overlaid (through translucency) on the presentation or be presented in a sidebar user interface. The additional data can be segmented in the same manner as the originally received data. If the additional data constitutes advertisements, or other content to be inserted into the program represented by the playlist, the additional data can be stored (at least temporarily) in operation 215, segmented in operation 225 and stored in operation 235; prior to storage of the segmented additional data, the segments of the additional data can be encrypted. Then in operation 245 an updated playlist, containing the program and the additional data, would be generated. The playlist is updated based on the additional data and stored again in operation 255. Changes to the playlist file(s) should be made atomically from the perspective of the client device. The updated playlist replaces, in one embodiment, the previous playlist. As discussed below in greater detail, client devices can request the playlist multiple times. These requests enable the client devices to utilize the most recent playlist. In one embodiment, the additional data may be metadata; in this case, the playlist does not need to be updated, but the segments can be updated to include metadata. For example, the metadata may contain timestamps which can be matched with timestamps in the segments, and the metadata can be added to segments having matching timestamps.

The updated playlist may also result in the removal of media files. In one embodiment, a server should remove URIs, for the media files, from the playlist in the order in which they were added to the playlist. In one embodiment, if the server removes an entire presentation, it makes the playlist file(s) unavailable to client devices. In one embodiment, the server maintains the media files and the playlist file(s) for the duration of the longest playlist file(s) containing a media file to be removed to allow current client devices to finish accessing the presentation. Accordingly, every media file URI in the playlist file can be prefixed with an EXT-X-STREAM-INF tag to indicate the approximate cumulative duration of the media files indicated by the playlist file. In alternate embodiments, the media files and the playlist file(s) may be removed immediately.

Subsequent requests for the playlist from client devices result in the server providing the updated playlist in operation 275. In one embodiment, playlists are updated on a regular basis, for example, a period of time related to the target duration. Periodic updates of the playlist file allow the server to provide access to servers to a dynamically changing presentation.

FIG. 2C is a flow diagram of one embodiment of a technique for one or more server devices to provide media content to client devices using multiple bit rates, which is one form of the use of alternative streams. The example of FIG. 2C is provided in terms of HTTP; however, other non-streaming protocols can be utilized in a similar manner. The example of FIG. 2C is provided in terms of a server performing certain tasks. However, any number of servers may be utilized. For example, the server that provides media files to client devices may be a different device than a server that segments the content into multiple media files.

In one embodiment, the server can offer multiple playlist files or a single playlist file with multiple media file lists in the single playlist file to provide different encodings of the same presentation. If different encodings are provided, playlist file(s) may include each variant stream providing different bit rates to allow client devices to switch between encodings dynamically (this is described further in connection with FIGS. 9A-9D). Playlist files having variant streams can include an EXT-X-STREAM-INF tag for each variant stream. Each EXT-X-STREAM-INF tag for the same presentation can have the same PROGRAM-ID attribute value. The PROGRAM-ID value for each presentation is unique within the variant streams.

In one embodiment, the server meets the following constraints when producing variant streams. Each variant stream can consist of the same content including optional content that is not part of the main presentation. The server can make the same period of content available for all variant streams within an accuracy of the smallest target duration of the streams. The media files of the variant streams are, in one embodiment, either MPEG-2 Transport Streams or MPEG-2 Program Streams with sample timestamps that match for corresponding content in all variant streams. Also, all variant streams should, in one embodiment, contain the same audio encoding. This allows client devices to switch between variant streams without losing content.

Referring to FIG. 2C, the server device receives content to be provided in operation 202. The server may then at least temporarily store the content in operation 212. The content to be provided is segmented into multiple media files in operation 222. Each media file is encoded for a selected bit rate (or a selected value of other encoding parameters) and stored on the server in operation 232. For example, the media files may be targeted for high-, medium- and low-bandwidth connections. The media files can be encrypted prior to storage. The encoding of the media files targeted for the various types of connections may be selected to provide a streaming experience at the target bandwidth level.

In one embodiment, a variant playlist is generated in operation 242 with tags as described herein that indicate various encoding levels. The tags may include, for example, an EXT-X-STREAM-INF tag for each encoding level with a URI to a corresponding media playlist file.

This variant playlist can include URIs to media playlist files for the various encoding levels. Thus, a client device can select a target bit rate from the alternatives provided in the variant playlist indicating the encoding levels and retrieve the corresponding playlist file. In one embodiment, a client device may change between bit rates during playback (e.g. as described with respect to FIGS. 9A-9D). The variant playlist indicating the various encoding levels is stored on the server in operation 252. In operation 242, each of the playlists referred to in the variant playlist can also be generated and then stored in operation 252.

In response to a request from a client device, the server may transmit the variant playlist that indicates the various encoding levels in operation 272. The server may receive a request for one of the media playlists specified in the variant playlist corresponding to a selected bit rate in operation 282. In response to the request, the server transmits the media playlist file corresponding to the request from the client device in operation 292. The client device may then use the media playlist to request media files from the server. The server provides the media files to the client device in response to requests in operation 297.

FIG. 3A is a flow diagram of one embodiment of a technique for a client device to support streaming of content using non-streaming protocols. The example of FIG. 3A is provided in terms of HTTP; however, other non-streaming protocols can be utilized in a similar manner. The methods shown in FIGS. 3A-3B can be performed by one client device or by several separate client devices. For example, in the case of any one of these methods, a single client device may perform all of the operations (e.g. request a playlist file, request media files using URIs in the playlist file, assemble the media files to generate and provide a presentation/output) or several distinct client devices can perform some but not all of the operations (e.g. a first client device can request a playlist file and request media files using URIs in the playlist file and can store those media files for use by a second client device which can process the media files to generate and provide a presentation/output).

The client device may request a playlist file from a server in operation 300. In one embodiment, the request is made according to an HTTP-compliant protocol. The request utilizes a URI to an initial playlist file stored on the server. In alternate embodiments, other non-streaming protocols can be supported. In response to the request, the server will transmit the corresponding playlist file to the client over a network. As discussed above, the network can be wired or wireless and can be any combination of wired or wireless networks. Further, the network may be a data network (e.g., IEEE 802.11, IEEE 802.16) or a cellular telephone network (e.g., 3G).

The client device can receive the playlist file in operation 310. The playlist file can be stored in a memory of the client device in operation 320. The memory can be, for example, a hard disk, a flash memory, a random-access memory. In one embodiment, each time a playlist file is loaded or reloaded from the playlist URI, the client checks to determine that the playlist file begins with a #EXTM3U tag and does not continue if the tag is absent. As discussed above, the playlist file includes one or more tags as well as one or more URIs to media files.

The client device can include an assembler agent that uses the playlist file to reassemble the original content by requesting media files indicated by the URIs in the playlist file in operation 330. In one embodiment, the assembler agent is a plug-in module that is part of a standard Web browser application. In another embodiment, the assembler agent may be a stand-alone application that interacts with a Web browser to receive and assemble the media files using the playlist file(s). As a further example, the assembler agent may be a special-purpose hardware or firmware component that is embedded in the client device.

The assembler causes media files from the playlist file to be downloaded from the server indicated by the URIs. If the playlist file contains the EXT-X-ENDLIST tag, any media file indicated by the playlist file may be played first. If the EXT-X-ENDLIST tag is not present, any media file except for the last and second-to-last media files may be played first. Once the first media file to play has been chosen, subsequent media files in the playlist file are loaded, in one embodiment, in the order that they appear in the playlist file (otherwise the content is presented out of order). In one embodiment, the client device attempts to load media files in advance of when they are required (and stores them in a buffer) to provide uninterrupted playback and to compensate for temporary variations in network latency and throughput.

The downloaded media file(s) can be stored in a memory on the client device in operation 340. The memory in which the content can be stored may be any type of memory on the client device, for example, random-access memory, a hard disk, or a video buffer. The storage may be temporary to allow playback or may be permanent. If the playlist file contains the EXT-X-ALLOW-CACHE tag and its value is NO, the client does not store the downloaded media files after they have been played. If the playlist contains the EXT-X-ALLOW-CACHE tag and its value is YES, the client device may store the media files indefinitely for later replay. The client device may use the value of the EXT-X-PROGRAM-DATE-TIME tag to display the program origination time to the user. In one embodiment, the client can buffer multiple media files so that it is less susceptible to network jitter, in order to provide a better user experience.

In one embodiment, if the decryption method is AES-128, then AES-128 CBC decryption is applied to the individual media files. The entire file is decrypted. In one embodiment, cipher block chaining is not applied across media files. The sequence number of the media file can be used as the initialization vector as described above.

From the memory, the content can be output from the client device in operation 350. The output or presentation may be, for example, audio output via built-in speakers or head phones. The output may include video that is output via a screen or projected from the client device. Any type of output known in the art may be utilized. In operation 351, the client device determines whether there are any more media files in the stored, current playlist which have not been played or otherwise presented. If such media files exist (and if they have not been requested) then processing returns to operation 330 in which one or more media files are requested and the process repeats. If there are no such media files (i.e., all media files in the current playlist have been played), then processing proceeds to operation 352, which determines whether the playlist file includes an end tag.

If the playlist includes an end tag (e.g., EXT-X-ENDLIST) in operation 352, playback ceases when the media files indicated by the playlist file have been played. If the end tag is not in the playlist, then the client device requests a playlist again from the server and reverts back to operation 300 to obtain a further or updated playlist for the program.

As discussed in greater detail with respect to FIG. 2B, a server may update a playlist file to introduce supplementary content (e.g., additional media file identifiers corresponding to additional media content in a live broadcast) or additional content (e.g. content further down the stream). To access the supplementary content or additional content, a client can reload the updated playlist from the server. This can provide a mechanism by which playlist files can be dynamically updated, even during playback of the media content associated with a playlist file. A client can request a reload of the playlist file based on a number of triggers. The lack of an end tag is one such trigger.

In one embodiment, the client device periodically reloads the playlist file(s) unless the playlist file contains the EXT-X-ENDLIST tag. When the client device loads a playlist file for the first time or reloads a playlist file and finds that the playlist file has changed since the last time it was loaded, the client can wait for a period of time before attempting to reload the playlist file again. This period is called the initial minimum reload delay. It is measured from the time that the client began loading the playlist file.

In one embodiment, the initial minimum reload delay is the duration of the last media file in the playlist file or three times the target duration, whichever is less. The media file duration is specified by the EXTINF tag. If the client reloads a playlist file and finds that it has not changed then the client can wait for a period of time before retrying. The minimum delay in one embodiment is three times the target duration or a multiple of the initial minimum reload delay, whichever is less. In one embodiment, this multiple is 0.5 for a first attempt, 1.5 for a second attempt and 3.0 for subsequent attempts; however, other multiples may be used.

Each time a playlist file is loaded or reloaded, the client device examines the playlist file to determine the next media file to load. The first file to load is the media file selected to play first as described above. If the first media file to be played has been loaded and the playlist file does not contain the EXT-X-MEDIA-SEQUENCE tag then the client can verify that the current playlist file contains the URI of the last loaded media file at the offset where it was originally found, halting playback if the file is not found. The next media file to load can be the first media file URI following the last-loaded URI in the playlist file.

If the first file to be played has been loaded and the playlist file contains the EXT-X-MEDIA-SEQUENCE tag, then the next media file to load can be the one with the lowest sequence number that is greater than the sequence number of the last media file loaded. If the playlist file contains an EXT-X-KEY tag that specifies a key file URI, the client device obtains the key file and uses the key inside the key file to decrypt the media files following the EXT-X-KEY tag until another EXT-X-KEY tag is encountered.

In one embodiment, the client device utilizes the same URI as previously used to download the playlist file. Thus, if changes have been made to the playlist file, the client device may use the updated playlist file to retrieve media files and provide output based on the media files.

Changes to the playlist file may include, for example, deletion of a URI to a media file, addition of a URI to a new media file, replacement of a URI to a replacement media file. When changes are made to the playlist file, one or more tags may be updated to reflect the change(s). For example, the duration tag may be updated if changes to the media files result in a change to the duration of the playback of the media files indicated by the playlist file.

FIG. 3B is a flow diagram of one embodiment of a technique for a client device to support streaming of content using multiple bit rates which is one form of alternative streams. The example of FIG. 3B is provided in terms of HTTP; however, other non-streaming protocols can be utilized in a similar manner.

The client device can request a playlist file in operation 370. As discussed above, the playlist file may be retrieved utilizing a URI provided to the client device. In one embodiment, the playlist file includes listings of variant streams of media files to provide the same content at different bit rates; in other words, a single playlist file includes URIs for the media files of each of the variant streams. The example shown in FIG. 3B uses this embodiment. In another embodiment, the variant streams may be represented by multiple distinct playlist files separately provided to the client that each provide the same content at different bit rates, and a variant playlist can provide a URI for each of the distinct playlist files. This allows the client device to select the bit rate based on client conditions.

The playlist file(s) can be retrieved by the client device in operation 375. The playlist file(s) can be stored in the client device memory in operation 380. The client device may select the bit rate to be used in operation 385 based upon current network connection speeds. Media files are requested from the server utilizing URIs included in the playlist file corresponding to the selected bit rate in operation 390. The retrieved media files can be stored in the client device memory. Output is provided by the client device utilizing the media files in operation 394 and the client device determines whether to change the bit rate.

In one embodiment, a client device selects the lowest available bit rate initially. While playing the media, the client device can monitor available bandwidth (e.g. current network connection bit rates) to determine whether the available bandwidth can support use of a higher bit rate for playback. If so, the client device can select a higher bit rate and access the media files indicated by the higher bit rate media playlist file. The reverse can also be supported. If the playback consumes too much bandwidth, the client device can select a lower bit rate and access the media files indicated by the lower bit rate media playlist file.

If the client device changes the bit rate in operation 394, for example, in response to a change in available bandwidth or in response to user input, the client device may select a different bit rate in operation 385. In one embodiment, to select a different bit rate the client device may utilize a different list of URIs included in the playlist file that corresponds to the new selected bit rate. In one embodiment, the client device may change bit rates during access of media files within a playlist.

If the bit rate does not change in operation 394, then the client device determines whether there are any more unplayed media files in the current playlist which have not been retrieved and presented. If such media files exist, then processing returns to operation 390 and one or more media files are retrieved using the URIs for those files in the playlist. If there are no such media files (i.e. all media files in the current playlist haven been played), then processing proceeds to operation 396 in which it is determined whether the playlist includes an end tag. If it does, the playback of the program has ended and the process has completed; if it does not, then processing reverts to operation 370, and the client device requests to reload the playlist for the program, and the process repeats through the method shown in FIG. 3B.

FIG. 4 is a block diagram of one embodiment of a server stream agent. It will be understood that the elements of server stream agent 400 can be distributed across several server devices. For example, a first server device can include the segmenter 430, the indexer 440 and security 450 but not the file server 460 and a second server device can include the file server 450 but not the segmenter 430, the indexer 440 and security 450. In this example, the first server device would prepare the playlists and media files but would not transmit them to client devices while one or more second server devices would receive and optionally store the playlists and media files and would transmit the playlists and media files to the client devices. Server stream agent 400 includes control logic 410, which implements logical functional control to direct operation of server stream agent 400, and hardware associated with directing operation of server stream agent 400. Logic may be hardware logic circuits or software routines or firmware. In one embodiment, server stream agent 400 includes one or more applications 412, which represent code sequence and/or programs that provide instructions to control logic 410.

Server stream agent 400 includes memory 414, which represents a memory device or access to a memory resource for storing data or instructions. Memory 414 may include memory local to server stream agent 400, as well as, or alternatively, including memory of the host system on which server stream agent 400 resides. Server stream agent 400 also includes one or more interfaces 416, which represent access interfaces to/from (an input/output interface) server stream agent 400 with regard to entities (electronic or human) external to server stream agent 400.

Server stream agent 400 also can include server stream engine 420, which represents one or more functions that enable server stream agent 400 to provide the real-time, or near real-time, streaming as described herein. The example of FIG. 4 provides several components that may be included in server stream engine 420; however, different or additional components may also be included. Example components that may be involved in providing the streaming environment include segmenter 430, indexer 440, security 450 and file server 460. Each of these components may further include other components to provide other functions. As used herein, a component refers to routine, a subsystem, etc., whether implemented in hardware, software, firmware or some combination thereof.

Segmenter 430 divides the content to be provided into media files that can be transmitted as files using a Web server protocol (e.g., HTTP). For example, segmenter 430 may divide the content into predetermined, fixed-size blocks of data in a pre-determined file format.

Indexer 440 may provide one or more playlist files that provide an address or URI to the media files created by segmenter 430. Indexer 440 may, for example, create one or more files with a listing of an order for identifiers corresponding to each file created by segmenter 430. The identifiers may be created or assigned by either segmenter 430 or indexer 440. Indexer 440 can also include one or more tags in the playlist files to support access and/or utilization of the media files.

Security 450 may provide security features (e.g. encryption) such as those discussed above. Web server 460 may provide Web server functionality related to providing files stored on a host system to a remote client device. Web server 460 may support, for example, HTTP-compliant protocols.

FIG. 5 is a block diagram of one embodiment of a client stream agent. It will be understood that the elements of a client stream agent can be distributed across several client devices. For example, a first client device can include an assembler 530 and security 550 and can provide a decrypted stream of media files to a second client device that includes an output generator 540 (but does not include an assembler 530 and security 550). In another example, a primary client device can retrieve playlists and provide them to a secondary client device which retrieves media files specified in the playlist and generates an output to present these media files. Client stream agent 500 includes control logic 510, which implements logical functional control to direct operation of client stream agent 500, and hardware associated with directing operation of client stream agent 500. Logic may be hardware logic circuits or software routines or firmware. In one embodiment, client stream agent 500 includes one or more applications 512, which represent code sequence or programs that provide instructions to control logic 510.

Client stream agent 500 includes memory 514, which represents a memory device or access to a memory resource for storing data and/or instructions. Memory 514 may include memory local to client stream agent 500, as well as, or alternatively, including memory of the host system on which client stream agent 500 resides. Client stream agent 500 also includes one or more interfaces 516, which represent access interfaces to/from (an input/output interface) client stream agent 500 with regard to entities (electronic or human) external to client stream agent 500.

Client stream agent 500 also can include client stream engine 520, which represents one or more functions that enable client stream agent 500 to provide the real-time, or near real-time, streaming as described herein. The example of FIG. 5 provides several components that may be included in client stream engine 520; however, different or additional components may also be included. Example components that may be involved in providing the streaming environment include assembler 530, output generator 540 and security 550. Each of these components may further include other components to provide other functions. As used herein, a component refers to routine, a subsystem, etc., whether implemented in hardware, software, firmware or some combination thereof.

Assembler 530 can utilize a playlist file received from a server to access the media files via Web server protocol (e.g., HTTP) from the server. In one embodiment, assembler 530 may cause to be downloaded media files as indicated by URIs in the playlist file. Assembler 530 may respond to tags included in the playlist file.

Output generator 540 may provide the received media files as audio or visual output (or both audio and visual) on the host system. Output generator 540 may, for example, cause audio to be output to one or more speakers and video to be output to a display device. Security 550 may provide security features such as those discussed above.

FIG. 6 illustrates one embodiment of a playlist file with multiple tags. The example playlist of FIG. 6 includes a specific number and ordering of tags. This is provided for description purposes only. Some playlist files may include more, fewer or different combinations of tags and the tags can be arranged in a different order than shown in FIG. 6.

Begin tag 610 can indicate the beginning of a playlist file. In one embodiment, begin tag 610 is a #EXTM3U tag. Duration tag 620 can indicate the duration of the playback list. That is, the duration of the playback of the media files indicated by playback list 600. In one embodiment, duration tag 620 is an EXT-X-TARGETDURATION tag; however, other tags can also be used.

Date/Time tag 625 can provide information related to the date and time of the content provided by the media files indicated by playback list 600. In one embodiment, Date/Time tag 625 is an EXT-X-PROGRAM-DATE-TIME tag; however, other tags can also be used. Sequence tag 630 can indicate the sequence of playlist file 600 in a sequence of playlists. In one embodiment, sequence tag 630 is an EXT-X-MEDIA-SEQUENCE tag; however, other tags can also be used.

Security tag 640 can provide information related to security and/or encryption applied to media files indicated by playlist file 600. For example, the security tag 640 can specify a decryption key to decrypt files specified by the media file indicators. In one embodiment, security tag 640 is an EXT-X-KEY tag; however, other tags can also be used. Variant list tag 645 can indicate whether variant streams are provided by playlist 600 as well as information related to the variant streams (e.g., how many, bit rate). In one embodiment, variant list tag 645 is an EXT-X-STREAM-INF tag.

Media file indicators 650 can provide information related to media files to be played. In one embodiment, media file indicators 650 include URIs to multiple media files to be played. In one embodiment, the order of the URIs in playlist 600 corresponds to the order in which the media files should be accessed and/or played. Subsequent playlist indictors 660 can provide information related to one or more playback files to be used after playback file 600. In one embodiment, subsequent playlist indicators 660 can include URIs to one or more playlist files to be used after the media files of playlist 600 have been played.

Memory tag 670 can indicate whether and/or how long a client device may store media files after playback of the media file content. In one embodiment, memory tag 670 is an EXT-X-ALLOW-CACHE tag. End tag 680 indicates whether playlist file 600 is the last playlist file for a presentation. In one embodiment, end tag 680 is an EXT-X-ENDLIST tag.

The following section contains several example playlist files according to one embodiment.

Simple Playlist file #EXTM3U #EXT-X-TARGETDURATION:10 #EXTINF:5220, http://media.example.com/entire.ts #EXT-X-ENDLIST Sliding Window Playlist, using HTTPS #EXTM3U #EXT-X-TARGETDURATION:8 #EXT-X-MEDIA-SEQUENCE:2680 #EXTINF:8, https://priv.example.com/fileSequence2680.ts #EXTINF:8, https://priv.example.com/fileSequence2681.ts #EXTINF:8, https://priv.example.com/fileSequence2682.ts Playlist file with encrypted media files #EXTM3U #EXT-X-MEDIA-SEQUENCE:7794 #EXT-X-TARGETDURATION:15 #EXT-X-KEY:METHOD=AES-128,URI=“ https://priv.example.com/key.php?r=52” #EXTINF:15, http://media.example.com/fileSequence7794.ts #EXTINF:15, http://media.example.com/fileSequence7795.ts #EXTINF:15, http://media.example.com/fileSequence7796.ts #EXT-X-KEY:METHOD=AES-128,URI=“ https://priv.example.com/key.php?r=53” #EXTINF:15, http://media.example.com/fileSequence7797.ts Variant Playlist file #EXTM3U #EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=1280000 http://example.com/low.m3u8 #EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=2560000 http://example.com/mid.m3u8 #EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=7680000 http://example.com/hi.m3u8 #EXT-X-STREAM-INF:PROGRAM- ID=1,BANDWIDTH=65000,CODECS=“mp4a.40.5” http://example.com/audio-only.m3u8

FIG. 7 is a flow diagram of one embodiment of a playback technique for assembled streams as described herein. In one embodiment, playback of the received media files can be controlled by the user to start, stop, rewind, etc. The playlist file is received by the client device in operation 700. The media files indicated by the playlist file are retrieved in operation 710. Output is generated based on the received media files in operation 720. Receiving and generating output based on media files can be accomplished as described above.

If control input is detected in operation 730, the client device can determine if the input indicates a stop in operation 740. If the input is a stop, the process concludes and playback stops. If the input indicates a rewind or forward request in operation 750, the client device can generate output based on previously played media files still stored in memory in operation 760. If these files are no longer in a cache, then processing reverts to operation 710 to retrieve the media files and repeats the process. In an alternate embodiment, playback can support a pause feature that halts playback without concluding playback as with a stop input.

Methods for transitioning from one stream to another stream are further described with reference to FIGS. 9A-9D. One client device can perform each of these methods or the operations of each of these methods can be distributed across multiple client devices as described herein; for example, in the distributed case, one client device can retrieve the variant playlist and the two media playlists and provide those to another client device which retrieves media files specified by the two media playlists and switches between the two streams provided by the retrieved media files. It will also be understood that, in alternative embodiments, the order of the operations shown may be modified or there can be more or fewer operations than shown in these figures. The methods can use a variant playlist to select different streams. A variant playlist can be retrieved and processed in operation 901 to determine available streams for a program (e.g. a sporting event). Operation 901 can be done by a client device. A first stream can be selected from the variant playlist in operation 903, and a client device can then retrieve a media playlist for the first stream. The client device can process the media playlist for the first stream in operation 905 and also measure or otherwise determine a bit rate of the network connection for the first stream in operation 907. It will be appreciated that the sequence of operations may be performed in an order which is different than what is shown in FIG. 9A; for example, operation 907 may be performed during operation 903, etc. In operation 911 the client device selects an alternative media playlist from the variant playlist based on the measured bit rate from operation 907; this alternative media playlist may be at a second bit rate that is higher than the existing bit rate of the first stream. This typically means that alternative stream will have a higher resolution than the first stream. The alternative media playlist can be selected if it is a better match than the current playlist for the first stream based on current conditions (e.g. the bit rate measured in operation 907). In operation 913, the alternative media playlist for an alternate stream is retrieved and processed. This typically means that the client device can be receiving and processing both the first stream and the alternative stream so both are available for presentation; one is presented while the other is ready to be presented. The client device then selects a transition point to switch between the versions of the streams in operation 915 and stops presenting the first stream and begins presenting the alternative stream. Examples of how this switch is accomplished are provided in conjunction with FIGS. 9B-9D. In some embodiments, the client device can stop receiving the first stream before making the switch.

FIG. 9B shows that the client device retrieves, stores and presents content specified by the first media playlist (e.g. the first stream) in operations 921 and 923, and while the content specified by the first playlist is being presented the client device in operation 925 also retrieves and stores content specified by the second media playlist (e.g. the second stream). The retrieval and storage (e.g. in a temporary buffer) of the content specified by the second media playlist while presenting the content obtained from the first media playlist creates an overlap 955 in time of the program's content (shown in FIG. 9D) that allows the client device to switch between the versions of the program without a substantial interruption of the program. In this way, the switch between the versions of the program can be achieved in many cases without the user noticing that a switch has occurred (although the user may notice a higher resolution image after the switch in some cases) or without a substantial interruption in the presentation of the program. In operation 927, the client device determines a transition point at which to switch from content specified by the first media playlist to content specified by the second media playlist; an example of a transition point (transition point 959) is shown in FIG. 9D. The content specified by the second media playlist is then presented in operation 931 after the switch.

The method shown in FIGS. 9C and 9D represents one embodiment for determining the transition point; this embodiment relies upon a pattern matching on audio samples from the two streams 951 and 953 to determine the transition point. It will be appreciated that alternative embodiments can use pattern matching on video samples or can use the timestamps in the two streams, etc. to determine the transition point. The method can include, in operation 941, storing content (e.g. stream 951) specified by the first media playlist in a buffer; the buffer can be used for the presentation of the content and also for the pattern matching operation. The stream 951 includes both audio samples 951A and video samples 951B. The video samples can use a compression technique which relies on i-frames or key frames which have all necessary content to display a single video frame. The content in stream 951 can include timestamps specifying a time (e.g. time elapsed since the beginning of the program), and these timestamps can mark the beginning of each of the samples (e.g. the beginning of each of the audio samples 951A and the beginning of each of the video samples 951B). In some cases, a comparison of the timestamps between the two streams may not be useful in determining a transition point because they may not be precise enough or because of the difference in the boundaries of the samples in the two streams; however, a comparison of the timestamps ranges can be used to verify there is an overlap 955 in time between the two streams. In operation 943, the client device stores in a buffer content specified by the second media playlist; this content is for the same program as the content obtained from the first media playlist and it can include timestamps also. In one embodiment, timestamps, if not present in a stream, can be added to a playlist for a stream; for example, in one embodiment an ID3 tag which includes one or more timestamps can be added to an entry in a playlist, such as a variant playlist or a media playlist. The entry may, for example, be in a URI for a first sample of an audio stream. FIG. 9D shows an example of content 953 obtained from the second media playlist, and this includes audio samples 953A and video samples 953B. In operation 945, the client device can perform a pattern matching on the audio samples in the two streams 951 and 953 to select from the overlap 955 the transition point 959 which can be, in one embodiment, the next self contained video frame (e.g. i-frame 961) after the matched audio segments (e.g. segments 957). Beginning with i-frame 961 (and its associated audio sample), presentation of the program uses the second stream obtained from the second media playlist. The foregoing method can be used in one embodiment for both a change from a slower to a faster bit rate and for a change from a faster to a slower bit rate, but in another embodiment the method can be used only for a change from a slower to a faster bit rate and another method (e.g. do not attempt to locate a transition point but attempt to store and present content from the slower bit rate stream as soon as possible) can be used for a change from a faster to a slower bit.

The following section of this description relates to the use of byte range requests in playlists that are described herein. Also, this section of this description describes methods of providing fast forward or rewind (reverse) playback from Iframes in the streaming media and the use of playlists with timing information that allows a cadence of Iframes to be selected when providing fast forward or rewind playback of the streaming media. The Iframes can be retrieved from a server using byte range requests.

The use of byte range requests in a playlist for 1× playback or in a playlist specifying Iframes for fast forward or rewind allows a provider to define multiple logical segments within a single large transport stream or elementary audio stream file. This can reduce the total number of files that must be managed at a server or other content distribution network and provides caching servers with more associativity information about the set of segments. An example of a media file, such as a movie, with multiple segments and with the ability to retrieve data from the file with byte range requests is shown in FIG. 13A. In one embodiment, cipher block chaining (CBC) and cryptographic padding can remain on a per-segment basis, such that CBC will restart on segment boundaries, such as the segment boundary between seg1.ts and seg2.ts shown in FIG. 13A. In one embodiment, the large file shown in FIG. 13A is essentially the concatenation of all of the individual segment files.

An example of a playlist syntax in one embodiment which uses byte range requests is as follows. A byte range tag is added to each segment specifier and has the form: #EXT-X-BYTERANGE:<length>[@<offset>] where <length> is the number of bytes in the segment and the optional parameter <offset> is the offset from the beginning of a file. If <offset> is omitted, the file offset is equal to the offset of previous entry plus its length. <offset> is assumed to be 0 for the first segment. An example of a Playlist specifying byte range segments in one embodiment is:

#EXTINF:10, #EXT-X-BYTERANGE:2390240@0 entire_movie.ts #EXTINF:10, #EXT-X-BYTERANGE:670416 entire_movie.ts #EXTINF:10, #EXT-X-BYTERANGE:465120 entire_movie.ts

Traditional playlists which can provide playback at a normal (1×) rate can use byte range requests to retrieve content from a single large transport stream or elementary audio stream file. Further, Iframe only playlists, which can be used to provide trick play mode playback, such as a fast forward or rewind playback (e.g. 8× or 16× or 32× or −8× or −16× or −32×), can also use byte range requests to retrieve content from a single large transport stream or elementary stream file.

In one embodiment, a variant playlist can include a URL for at least one 1× playback playlist and a URL for at least one Iframe playlist; in a typical implementation, a variant playlist can have a plurality of URLs for 1× playlists, each at different bandwidths or other variations such as different codecs, etc. and can also contain a plurality of URLs for Iframe playlists at different bandwidths or other variations, such as different codecs, etc. FIG. 10 shows an example of a variant playlist 1001 containing both URLs for traditional 1× playback playlists as well as a plurality of URLs for Iframe playlists, which in this case are Iframe only playlists. In particular, URL 1003 is a URL for a IX playback playlist at bandwidth X and URL 1005 is a URL for a IX playback playlist at bandwidth Y. URL 1007 is a URL for an Iframe only playlist at bandwidth X and URL 1009 is a URL for an Iframe only playlist at bandwidth Y. This entire playlist file 1001 is provided in response to a request from a client to view a particular movie or video on demand or other content, and in response to that request, a server provides the playlist file 1001 containing the two different sets of URLs, allowing either 1× playback or fast forward or reverse playback. This allows a client device to receive the variant playlist and to store that variant playlist and then be able to switch between 1× playback or fast forward or reverse playback by selectively choosing the appropriate playlist file in the variant playlist. Typically, Iframe playlists will make use of the byte range feature discussed herein. The byte range feature provides information about the location of Iframes within segments, and this allows a client device to rapidly scan backward or forward through both video on demand and live presentations by only fetching and displaying Iframes, and it does not require special-purpose media files for the different playback speeds. In one embodiment, the client device can adaptively switch between variants of the Iframe playlists when displaying Iframes to provide the best user experience based upon the current network speed; in other words, the network speed can be dynamically determined while performing fast forward or reverse playback and the client system can adaptively switch in response to the dynamically determined network speed between the variants of the Iframe playlists contained within the variant playlist. An example of a variant playlist containing Iframe playlists is:

#EXTM3U #EXT-X-VERSION:4 #EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=326448 BTBW0.2Mb/prog_index.m3u8 #EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=1255635 BTBW0.8Mb/prog_index.m3u8 #EXT-X-I-FRAME-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=75915 BTBW0.2Mb/iframes.m3u8 #EXT-X-I-FRAME-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=380752 BTBW0.8Mb/iframes.m3u8 The #EXT-X-I-FRAME-STREAM-INF tag has the same set of attributes that the #EXT-X-STREAM-INF (PROGRAM-ID, BANDWIDTH, CODECS) It can be seen from this variant playlist, that the variant playlist provides two versions for 1× playback at different bandwidths and two versions of the Iframe playlists also at two different bandwidths. In one embodiment, the Iframe playlists contain byte range requests for only Iframes within the media file, and hence the Bframes and Pframes are not included within these byte range requests which are specified in the Iframe only playlists.

An example of an Iframe only playlist is: (note the EXT-X-I-FRAMES-ONLY tag):

#EXTM3U #EXT-X-TARGETDURATION:10 #EXT-X-VERSION:4 #EXT-X-MEDIA-SEQUENCE:0 #EXT-X-I-FRAMES-ONLY #EXTINF:1.2489, #EXT-X-BYTERANGE:1505@376 segment0.ts #EXTINF:4.9633, #EXT-X-BYTERANGE:1505@125584 segment0.ts #EXTINF:5.005, #EXT-X-BYTERANGE:37413@539184 segment0.ts #EXTINF:5.005, #EXT-X-BYTERANGE:30645@152844 segment1.ts Note that the byte range only includes the Iframe; to read the PAT/PMT, the client will read from the beginning of the first URL in a discontinuity domain to the offset of the first Iframe. In this embodiment, the byte range request is specified in a tag that is adjacent to its corresponding URL but is not part of the URL, although in another embodiment, the byte range request can be part of the URL. As can be seen from this Iframe playlist, a new tag has been added to a regular playlist, indicating that the segment specifiers refer to Iframes, and that the EXTINF durations refer to the span of time between that Iframe and the next Iframe. The use of this time information will be described in connection with the methods shown in FIGS. 14 and 15.

FIG. 11 is a flowchart which shows a method in one embodiment for creating the variant playlist shown in FIG. 10 or other variant playlists containing references to Iframe playlists. In operation 1101, a data processing system determines the Iframes in the video content. Well-known techniques can be employed to determine the Iframes in the file or transport stream. In operation 1103, an Iframe playlist, such as an Iframe only playlist, can be created by a data processing system and, in addition, a variant playlist containing URLs for the Iframe playlist and optionally a 1× playlist is then created. The data processing system can also create the 1× playlist in addition to the variant playlist and the Iframe playlist. The Iframe playlist can include a plurality of URLs for a plurality of 1× playlists and can also include a plurality of URLs for corresponding plurality of Iframe playlists. An example of such a variant playlist is shown in FIG. 10. In response to a request from a client device to view a program, the data processing system or another data processing system can transmit the variant playlist which contains the URLs for the 1× playlist or playlists and for the Iframe playlist or playlists. The transmission of the variant playlist is shown as operation 1105 in FIG. 11. Then, the same server system or another server system waits for a client request for either the Iframe playlist or a 1× playlist. In operation 1107 and in operation 1109, a transmission server determines whether a client has requested an Iframe playlist or a 1× playlist based upon the request received from the client, and in response, the transmission server transmits either the Iframe playlist in operation 1113 or transmits the 1× playlist in operation 1111.

FIG. 12 shows an example of an architecture for a client device which can implement either of the methods shown in FIGS. 14 and 15. The components shown in client device 1201 can be software components (running on a data processing system such as the system shown in FIG. 8) or hardware components or a combination of software and hardware components. In one embodiment, the user application 1207 is a software application run by the user to display a movie or a baseball game or listen to a radio show, etc. For example, in one embodiment, the user application can be an app provided by Major League Baseball to view baseball games. The app 1207 can interact with a player module 1209 which can also be a software program operating on a data processing system, such as the system shown in FIG. 8. User application 1207 interacts with the player module 1209 through, in one embodiment, an API described further herein. Similarly, the player module 1209 can interact with a download and data rate measurement module 1211 through APIs. The player module 1209 can, in one embodiment, process playlists in order to instruct the download module to download content from URLs provided to the download module. The download module 1211 can perform the download operations through one or more network interfaces 1213 which are coupled to one or more networks, such as network 1203, which in turn are coupled to one or more servers 1205, such as content servers or servers providing playlists and content, etc. The download and data rate measurement module 1211 also performs a data rate measurement when retrieving content specified in the playlist. The data rate measurement can be used in the methods described in conjunction with FIGS. 14 and 15 in determining the appropriate cadence of Iframes to download in order to provide fast forward or rewind (reverse) playback, otherwise known as trick play playback mode.

FIGS. 13A and 13B will now be referred to while describing the relationship between a media file and its associated Iframe playlist. It will be seen that the Iframe playlist includes metadata about the media file which allows the methods shown in FIGS. 14 and 15 to be performed in order to select a subset or cadence of Iframes in order to provide fast forward or rewind playback (e.g. 8× or 16× or 32× playback or rewind playback at −8× or −16× or −32×). Media file 1301 can be a movie or a video on demand or a live broadcast or other file created according to the HTTP live streaming protocol that is known in the art. The media file 1301 includes a plurality of Iframes as is known in the art. The Iframes 1305 include Iframes I₀, I₁, I₂, I₃, I₄, I₅, and I₆. Each Iframe, as is known in the art, is followed by Bframes and Pframes which require the Iframe in order to decode the content in the Bframes and the Pframes. As can be seen from FIG. 13A, the Iframes are not evenly distributed in time through the file due to the nature of the motion within the video as is known in the art. Metadata within media file 1301 can include segment information 1303 which specifies different segments in time which are used for cipher block chaining and cryptographic padding as is known in the art. Cipher block chaining will restart on segment boundaries in one embodiment. The media file 1301 is essentially the concatenation of all of the individual segment files. The media file 1301 can include time metadata 1307 which represents a span of time between the beginning of each consecutive Iframe. For example, the time 7.3 seconds at the beginning of Iframe I₁ means that Iframe I₀ and its associated B and P frames occupy a duration in time of 7.3 seconds. The time metadata 1307 shown below the Iframes in FIG. 13A is a value of time; for example, Iframe 6 is displayed 26 seconds into the movie's normal 1× playback time. Similarly, Iframe 4 is presented at 16.2 seconds in movie time when the movie is played at 1× playback rate. In one embodiment, the time metadata shown below the Iframes in FIG. 13A can be included in the media file 1301, while in other embodiments it may be derived from the media file without being stored with the media file, but the time metadata will be used, as explained below, in the Iframe playlist, such as the Iframe playlist shown in FIG. 13B and this time metadata can be used in the methods of FIG. 14 or 15.

The Iframe playlist shown in FIG. 13B represents a portion of the Iframe playlist for the media file 1301 shown in FIG. 13A. This playlist includes an Iframe only specifier 1315 which indicates that the playlist is for Iframes only. The tag #EXTINF: 7.3 is a span duration for Iframe I₀; in other words, span duration 1317 represents the span in time of Iframe I₀ and matches the 7.3 shown at the beginning of Iframe I₁. Byte range request 1319 includes a byte range parameter that specifies byte range A shown in FIG. 13A; in other words, the byte range parameter in byte range request 1319 specifies the range of data to retrieve only the Iframe I₀ from the media file 1301. Segment specifiers 1321 and 1327 specify the particular segment in which the bytes are located. Byte range request 1323 also includes a span duration which, in this case, is 2.5 which matches the difference between 9.8 seconds and 7.3 seconds shown in FIG. 13A. In particular, 2.5 seconds specifies the duration between the beginning of Iframe I₁ and the beginning of Iframe I₂. Byte range request 1325 includes a byte range parameter that specifies the byte range B shown in FIG. 13A in order to retrieve the video content for Iframe I₁. It will be appreciated that in some embodiments, audio data may be multiplexed with the video data within the same byte range, but that audio data is typically not used in fast forward or reverse playback. The span durations 1317 and 1323 can be used, in one embodiment, in order to determine the amount of time available to download different cadences of Iframes as is described further below in conjunction with FIG. 14 or FIG. 15.

FIG. 14 shows a method for determining a set of Iframes from all available Iframes that are available before a display deadline. The method shown in FIG. 14 is performed on a client device (e.g. the client device 1201) which has received an Iframe playlist, such as the Iframe playlist 13B and is in the process of processing that Iframe playlist in order to provide fast forward or reverse playback through the use of the Iframe playlist. A set can be selected from all of the available Iframes before the display deadline in such a fashion that the Iframes are at least somewhat evenly distributed over time. In operation 1401, the client device determines a plurality of sets of available Iframes in the Iframe playlists; the sets are based on the current movie time, the selected playback mode, such as 8× or 16× or −8×, etc., and a display deadline. In one embodiment, the display deadline can be based upon a real time clock of the current time plus a fixed value of time, such as a half a second or one second or two seconds from the current real time clock time. A player time or movie time can be derived from this display deadline based upon the playback rate; for example, if the playback rate is 16× then 16 seconds can be added to the time span duration for the current Iframe to give a player time at the display deadline. For example, if the playback rate is 8× and the currently displayed Iframe is I₀ shown in FIG. 13A, then 8 seconds (corresponding to 8× playback rate) can be added to 7.3 seconds to derive a player time (or movie time) at the display deadline. The player time at the display deadline effectively sets a maximum number of Iframes which can be retrieved by the display deadline; that maximum number of Iframes is the number of Iframes between the currently displayed Iframe and the last full Iframe before the display deadline. Different playback rates will produce different display deadlines as is shown in FIG. 16. FIG. 16 shows an example of a media file having at least 17 Iframes which begin, in time, with Iframe I₀ and end with Iframe I₁₇ as shown in FIG. 16. The currently displayed Iframe is Iframe I₀ and time progresses from left to right. If playback rate is set at 16×, then the display deadline is at or before Iframe I₅₀, while if the playback rate is set at 32×, then the display deadline is set at on or before Iframe I₁₇. Hence, in the case of FIG. 16, the maximum number of Iframes which can be retrieved prior to the display deadline is 9 Iframes (Iframes I₁-I₉) if the playback rate is 16×, while the maximum number of frames that could be available to be downloaded is 16 Iframes (Iframes I₁-I₁₆) when the playback rate is set at 32×. Hence, operation 1401 in operation 14 determines a maximum number of Iframes which can be downloaded given the display deadline and the currently selected playback rate and the current movie time, and then proceeds to determine subsets of those available Iframes. In one embodiment, those subsets could be every other Iframe in time or every third Iframe in time, etc.

Then in operation 1403, the client device determines the download times for each set of available Iframes. Normally, each set of available Iframes will have a different number of Iframes and so their download times will vary. For example, the client device could determine the download time for downloading every other Iframe in the maximum number of Iframes which are available and determine the download time for every third Iframe in the maximum number of Iframes which are available to download before the display deadline, etc. Then in operation 1405, the client device selects one of the sets of available Iframes that can be downloaded before the display deadline, and then in operation 1407, the client device downloads the selected set of available Iframes and displays them. In one embodiment, the client device will download each Iframe one at a time and repeat the processing operations of 1401, 1403, and 1405 based upon the actual download time of the last Iframe. It will be appreciated that during the fast forward or rewind playback, the user may desire to stop playback or may change the speed of the playback, and this is represented as operation 1409 in which the system determines whether the content is over or has been stopped or the user has changed the playback speed, etc. The client device will respond based upon the user input.

In one embodiment, the method of the present invention can continually evaluate the download times while presenting Iframes in a fast forward or reversed mode, and the client device can automatically determine, without user intervention, whether or not to change resolution or quality. For example, if a user has selected 8× and the network speed is fast, then the Iframes are being downloaded sufficiently fast such that there is spare time which could be used to download higher resolution Iframes, then the system could automatically switch to a different Iframe playlist after determining, in operation 1411, to change resolution or quality, and then do so in operation 1413 in which the client device changes to a different Iframe playlist which has, in this case, higher resolution or better image quality. FIG. 18 shows an example of a method which includes operations 1801, 1803, and 1805 that switch between Iframe playlists. In one embodiment, the client device may present a user interface to the user, asking the user to confirm the change of resolution or quality before doing so. The change in resolution or quality could either be an increased resolution or quality when the network bandwidth is high or a change to a lower resolution or quality when the network bandwidth is poor or low. The method shown in FIG. 14 continues with operation 1415 in which the next current movie time is determined and the next display deadline is determined and then the process repeats by reverting back to operation 1401.

FIG. 15 shows further details in connection with the method of processing an Iframe playlist in order to provide fast forward or reverse playback. It will be understood that the method of FIG. 15 can include operations in which the user stops the playback or decides to change the playback rate or the system changes the resolution or quality; for example, operations 1409 and 1411 can also be performed at any time within the method shown in FIG. 15. Further, it will be understood that the order of the operations may be different than the order shown in FIG. 15 in alternative embodiments. The method of FIG. 15 assumes that a client device has downloaded an Iframe playlist, such as an Iframe playlist which is specified in a variant playback (e.g., the playlist shown in FIG. 10). It will also be appreciated that the method of FIG. 15 may be implemented with the client device shown in FIG. 12 which includes a download measurement module that measures the download rate of data, such as a byte range of data corresponding to a particular Iframe, such as the last Iframe which was downloaded. In operation 1501, the client device determines the current movie time of the beginning of the currently displayed Iframe, and this current movie time may be denoted T_(C). In the example shown in FIG. 10, Iframe I₀ is the current Iframe being displayed, and the client device will determine the current movie time of the beginning of that Iframe I₀. Then in operation 1503, the client device determines the current playback mode which can be any one of a variety of different fast forward or reverse speeds, such as 8× or 16× or −8×, etc. Then in operation 1505, the client device determines the current display deadline. In one embodiment, this can be performed by adding a multiple (e.g. a multiple of 1 or 2) of the current playback rate to the current movie time. For example, if the multiple is one second and the current playback rate is 8×, then a product of one second times 8 seconds produces 8 seconds and that product is added to the current movie time T₀ to produce the current display deadline. This current display deadline can be in movie time and can set a boundary which determines the maximum number of Iframes that are available before the current display deadline. This operation is shown as operation 1507 in FIG. 15. In the example shown in FIG. 16, if the playback rate is 16×, then the client device will determine that all Iframes that are available before the current display deadline in operation 1507 corresponds to Iframes I₁ through I₉ shown in FIG. 16. Then in operation 1509, the client device determines subsets of all of those Iframes determined in operation 1507. In other words, the client device will determine the various subsets of those Iframes that are available before the current display deadline. In one embodiment, each of those subsets can have a different cadence and each cadence can have a different number of Iframes. In one embodiment, the cadence can be designed such that the Iframes are evenly distributed over time or at least evenly distributed over the sequence of available Iframes (and not necessarily perfectly over time).

FIGS. 17A, 17B, 17C, and 17D show examples of four different cadences. FIG. 17A represents a cadence in which every one of the Iframes in the set of all Iframes determined in operation 1507 is being considered for download. The cadence shown in FIG. 17B represents a cadence (in this case, a subset of Iframes) in which every other one of the Iframes that were determined to be available for download in operation 1507 is considered for downloading. Similarly, the cadence shown in FIG. 17C is every third Iframe, and the cadence shown in FIG. 17D is every fourth Iframe in the group of Iframes that are available as determined in operation 1507. In one embodiment, as shown in operation 1511, the client device can optionally limit the number of Iframes within each subset to a fixed or predetermined number or to a number which can be varied by the user or the system. The limiting of the number of Iframes in this manner can improve the user experience in some embodiments. Then in operation 1513, the client device determines the download times for each of the subset of Iframes, each having, in one embodiment, a different cadence, such as the different cadences shown in FIGS. 17A through 17D. The download times for each cadence in the set of cadences can be derived from the download time of the last Iframe currently being displayed or a running average which exponentially decays over time of the last two or three or four or more Iframes which have been downloaded or a smoothed average of the last two or three or more Iframes which have been downloaded. The measurement of the download time can be performed by module 1211 shown in FIG. 12, and those download times can be provided to the player module 1209 which can perform the selection of one of the subset of Iframes in operation 1515. The client device will, in operation 1515, determine whether each of the cadences can be downloaded prior to the display deadline, and for those which cannot it will discard those as the possible solution and will select a cadence which has the highest number of Iframes and which can be downloaded within the period of time before the current display deadline. Again, in one embodiment, the selected cadence can be limited in operation 1511 to a maximum number of Iframes in a period of time, such as no more than 10 Iframes per second and this can improve the visual experience of trick play. After the particular cadence has been selected in operation 1515, the client device can begin to download the first Iframe in the selected subset. In one embodiment, the client device can optionally first check whether it is too late to download that Iframe and if it is, skip to the next Iframe in the cadence that was selected in operation 1515. In one embodiment, the player module 1209 performs the selection in operation 1515 and then requests the download module 1211 to download that first Iframe in operation 1517. The download module can then measure the download rate or download time of that Iframe and that information can then be used in the next iteration through the method of FIG. 15 which occurs when operation 1517 is followed by operation 1501. If network conditions change (e.g., network bandwidth drops such that download times become longer) then the method of FIG. 15 can be performed again before downloading all of the Iframes in the selected cadence and hence the cadence can change before the client device completes the downloading of the Iframes in the last selected cadence. Should this continue to happen, the client device can decide, as shown in FIG. 18, to change the resolution or quality of the Iframes in order to adjust to the slowing network. Alternatively, if the network speed increases, the method of FIG. 18 may also be used to change the resolution or quality of the Iframes. As noted above, the method of FIG. 18 may be performed at any time automatically by the system or in response to user requests in certain cases.

FIG. 8 is a block diagram of one embodiment of an electronic system. The electronic system illustrated in FIG. 8 is intended to represent a range of electronic systems (either wired or wireless) including, for example, desktop computer systems, laptop computer systems, cellular telephones, personal digital assistants (PDAs) including cellular-enabled PDAs, set top boxes, entertainment systems or other consumer electronic devices. Alternative electronic systems may include more, fewer and/or different components. The electronic system of FIG. 8 may be used to provide the client device and/or the server device.

Electronic system 800 includes bus 805 or other communication device to communicate information, and processor 810 coupled to bus 805 that may process information. While electronic system 800 is illustrated with a single processor, electronic system 800 may include multiple processors and/or co-processors. Electronic system 800 further may include random access memory (RAM) or other dynamic storage device 820 (referred to as main memory), coupled to bus 805 and may store information and instructions that may be executed by processor 810. Main memory 820 may also be used to store temporary variables or other intermediate information during execution of instructions by processor 810.

Electronic system 800 may also include read only memory (ROM) and/or other static storage device 830 coupled to bus 805 that may store static information and instructions for processor 810. Data storage device 840 may be coupled to bus 805 to store information and instructions. Data storage device 840 such as flash memory or a magnetic disk or optical disc and corresponding drive may be coupled to electronic system 800.

Electronic system 800 may also be coupled via bus 805 to display device 850, such as a cathode ray tube (CRT) or liquid crystal display (LCD), to display information to a user. Electronic system 800 can also include an alphanumeric input device 860, including alphanumeric and other keys, which may be coupled to bus 805 to communicate information and command selections to processor 810. Another type of user input device is cursor control 870, such as a touchpad, a mouse, a trackball, or cursor direction keys to communicate direction information and command selections to processor 810 and to control cursor movement on display 850.

Electronic system 800 further may include one or more network interface(s) 880 to provide access to a network, such as a local area network. Network interface(s) 880 may include, for example, a wireless network interface having antenna 885, which may represent one or more antenna(e). Electronic system 800 can include multiple wireless network interfaces such as a combination of WiFi, Bluetooth and cellular telephony interfaces. Network interface(s) 880 may also include, for example, a wired network interface to communicate with remote devices via network cable 887, which may be, for example, an Ethernet cable, a coaxial cable, a fiber optic cable, a serial cable, or a parallel cable.

In one embodiment, network interface(s) 880 may provide access to a local area network, for example, by conforming to IEEE 802.11b and/or IEEE 802.11g standards, and/or the wireless network interface may provide access to a personal area network, for example, by conforming to Bluetooth standards. Other wireless network interfaces and/or protocols can also be supported.

In addition to, or instead of, communication via wireless LAN standards, network interface(s) 880 may provide wireless communications using, for example, Time Division, Multiple Access (TDMA) protocols, Global System for Mobile Communications (GSM) protocols, Code Division, Multiple Access (CDMA) protocols, and/or any other type of wireless communications protocol.

One or more Application Programming Interfaces (APIs) may be used in some embodiments. An API is an interface implemented by a program code component or hardware component (hereinafter “API-implementing component”) that allows a different program code component or hardware component (hereinafter “API-calling component”) to access and use one or more functions, methods, procedures, data structures, classes, and/or other services provided by the API-implementing component. An API can define one or more parameters that are passed between the API-calling component and the API-implementing component.

An API allows a developer of an API-calling component (which may be a third party developer) to leverage specified features provided by an API-implementing component. There may be one API-calling component or there may be more than one such component. An API can be a source code interface that a computer system or program library provides in order to support requests for services from an application. An operating system (OS) can have multiple APIs to allow applications running on the OS to call one or more of those APIs, and a service (such as a program library) can have multiple APIs to allow an application that uses the service to call one or more of those APIs. An API can be specified in terms of a programming language that can be interpreted or compiled when an application is built.

In some embodiments the API-implementing component may provide more than one API, each providing a different view of or with different aspects that access different aspects of the functionality implemented by the API-implementing component. For example, one API of an API-implementing component can provide a first set of functions and can be exposed to third party developers, and another API of the API-implementing component can be hidden (not exposed) and provide a subset of the first set of functions and also provide another set of functions, such as testing or debugging functions which are not in the first set of functions. In other embodiments the API-implementing component may itself call one or more other components via an underlying API and thus be both an API-calling component and an API-implementing component.

An API defines the language and parameters that API-calling components use when accessing and using specified features of the API-implementing component. For example, an API-calling component accesses the specified features of the API-implementing component through one or more API calls or invocations (embodied for example by function or method calls) exposed by the API and passes data and control information using parameters via the API calls or invocations. The API-implementing component may return a value through the API in response to an API call from an API-calling component. While the API defines the syntax and result of an API call (e.g., how to invoke the API call and what the API call does), the API may not reveal how the API call accomplishes the function specified by the API call. Various API calls are transferred via the one or more application programming interfaces between the calling (API-calling component) and an API-implementing component. Transferring the API calls may include issuing, initiating, invoking, calling, receiving, returning, or responding to the function calls or messages; in other words, transferring can describe actions by either of the API-calling component or the API-implementing component. The function calls or other invocations of the API may send or receive one or more parameters through a parameter list or other structure. A parameter can be a constant, key, data structure, object, object class, variable, data type, pointer, array, list or a pointer to a function or method or another way to reference a data or other item to be passed via the API.

Furthermore, data types or classes may be provided by the API and implemented by the API-implementing component. Thus, the API-calling component may declare variables, use pointers to, use or instantiate constant values of such types or classes by using definitions provided in the API.

Generally, an API can be used to access a service or data provided by the API-implementing component or to initiate performance of an operation or computation provided by the API-implementing component. By way of example, the API-implementing component and the API-calling component may each be any one of an operating system, a library, a device driver, an API, an application program, or other module (it should be understood that the API-implementing component and the API-calling component may be the same or different type of module from each other). API-implementing components may in some cases be embodied at least in part in firmware, microcode, or other hardware logic. In some embodiments, an API may allow a client program to use the services provided by a Software Development Kit (SDK) library. In other embodiments an application or other client program may use an API provided by an Application Framework. In these embodiments the application or client program may incorporate calls to functions or methods provided by the SDK and provided by the API or use data types or objects defined in the SDK and provided by the API. An Application Framework may in these embodiments provide a main event loop for a program that responds to various events defined by the Framework. The API allows the application to specify the events and the responses to the events using the Application Framework. In some implementations, an API call can report to an application the capabilities or state of a hardware device, including those related to aspects such as input capabilities and state, output capabilities and state, processing capability, power state, storage capacity and state, communications capability, etc., and the API may be implemented in part by firmware, microcode, or other low level logic that executes in part on the hardware component.

The API-calling component may be a local component (i.e., on the same data processing system as the API-implementing component) or a remote component (i.e., on a different data processing system from the API-implementing component) that communicates with the API-implementing component through the API over a network. It should be understood that an API-implementing component may also act as an API-calling component (i.e., it may make API calls to an API exposed by a different API-implementing component) and an API-calling component may also act as an API-implementing component by implementing an API that is exposed to a different API-calling component.

The API may allow multiple API-calling components written in different programming languages to communicate with the API-implementing component (thus the API may include features for translating calls and returns between the API-implementing component and the API-calling component); however the API may be implemented in terms of a specific programming language. An API-calling component can, in one embedment, call APIs from different providers such as a set of APIs from an OS provider and another set of APIs from a plug-in provider and another set of APIs from another provider (e.g. the provider of a software library) or creator of the another set of APIs.

FIG. 19 is a block diagram illustrating an exemplary API architecture, which may be used in some embodiments of the invention. As shown in FIG. 19, the API architecture 1800 includes the API-implementing component 1810 (e.g., an operating system, a library, a device driver, an API, an application program, software or other module) that implements the API 1820. The API 1820 specifies one or more functions, methods, classes, objects, protocols, data structures, formats and/or other features of the API-implementing component that may be used by the API-calling component 1830. The API 1820 can specify at least one calling convention that specifies how a function in the API-implementing component receives parameters from the API-calling component and how the function returns a result to the API-calling component. The API-calling component 1830 (e.g., an operating system, a library, a device driver, an API, an application program, software or other module), makes API calls through the API 1820 to access and use the features of the API-implementing component 1810 that are specified by the API 1820. The API-implementing component 1810 may return a value through the API 1820 to the API-calling component 1830 in response to an API call.

It will be appreciated that the API-implementing component 1810 may include additional functions, methods, classes, data structures, and/or other features that are not specified through the API 1820 and are not available to the API-calling component 1830. It should be understood that the API-calling component 1830 may be on the same system as the API-implementing component 1810 or may be located remotely and accesses the API-implementing component 1810 using the API 1820 over a network. While FIG. 19 illustrates a single API-calling component 1830 interacting with the API 1820, it should be understood that other API-calling components, which may be written in different languages (or the same language) than the API-calling component 1830, may use the API 1820.

The API-implementing component 1810, the API 1820, and the API-calling component 1830 may be stored in a machine-readable non-transitory storage medium, which includes any mechanism for storing information in a form readable by a machine (e.g., a computer or other data processing system). For example, a machine-readable medium includes magnetic disks, optical disks, random access memory; read only memory, flash memory devices, etc.

In FIG. 20 (“Software Stack”), an exemplary embodiment, applications can make calls to Services 1 or 2 using several Service APIs and to Operating System (OS) using several OS APIs. Services 1 and 2 can make calls to OS using several OS APIs.

Note that the Service 2 has two APIs, one of which (Service 2 API 1) receives calls from and returns values to Application 1 and the other (Service 2 API 2) receives calls from and returns values to Application 2. Service 1 (which can be, for example, a software library) makes calls to and receives returned values from OS API 1, and Service 2 (which can be, for example, a software library) makes calls to and receives returned values from both OS API 1 and OS API 2. Application 2 makes calls to and receives returned values from OS API 2.

Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. 

1. A machine readable non-transitory storage medium storing executable instructions which, when executed, cause a data processing system to perform a method comprising: receiving a first playlist that includes a URL for a second playlist and a URL for a third playlist, the second playlist including a plurality of URLs specifying portions of a file containing I-frames, and the third playlist including a plurality of URLs to display a video at a 1× speed; determining a playback speed which is other than 1×; transmitting the URL for the second playlist in response to determining the playback speed; receiving the second playlist; transmitting requests for I-frames using URLs in the second playlist; presenting, at the playback speed, I-frames that are received in response to the request for I-frames; and wherein the URLs in the second playlist are associated with parameters specifying a range of data for each I-frame in the file containing the I-frames.
 2. The medium as in claim 1 wherein tags associated with the URLs in the third playlist include parameters specifying a range of data in the file containing the video.
 3. The medium as in claim 1 wherein the first playlist includes a plurality of URLs, for a corresponding plurality of 1× playlists, to display the video at the 1× speed at either different resolutions or different qualities and the first playlist includes a plurality of URLs, for a corresponding plurality of I-frame only playlists, at either different resolutions or different qualities.
 4. The medium as in claim 3 wherein the second playlist has tags, associated with or adjacent to their corresponding URLs, which specify portions of the file containing only I-frames.
 5. The medium as in claim 3 wherein each of the URLs in the second playlist has a movie time metadata associated with the URL.
 6. The medium as in claim 5 wherein the range of data for each I-frame is specified by a byte range and wherein each byte range includes audio data which is not used when playback is at the playback speed.
 7. A data processing system comprising: means for receiving a first playlist that includes a URL for a second playlist and a URL for a third playlist, the second playlist including a plurality of URLs specifying portions of a file containing I-frames, and the third playlist including a plurality of URLs to display a video at a 1× speed; means for determining a playback speed which is other than 1×; means for transmitting the URL for the second playlist in response to determining the playback speed; means for receiving the second playlist; means for transmitting requests for I-frames using URLs in the second playlist; means for presenting, at the playback speed, I-frames that are received in response to the request for I-frames; and wherein the URLs in the second playlist are associated with parameters specifying a range of data for each I-frame in the file containing the I-frames.
 8. The system as in claim 7 wherein tags associated with the URLs in the third playlist include parameters specifying a range of data in the file containing the video.
 9. The system as in claim 7 wherein the first playlist includes a plurality of URLs, for a corresponding plurality of 1× playlists, to display the video at the 1× speed at either different resolutions or different qualities and the first playlist includes a plurality of URLs, for a corresponding plurality of I-frame only playlists, at either different resolutions or different qualities.
 10. The system as in claim 9 wherein the second playlist has tags, associated with or adjacent to their corresponding URLs, which specify portions of the file containing only I-frames.
 11. The system as in claim 9 wherein each of the URLs in the second playlist has a movie time metadata associated with the URL and wherein the range of data for each I-frame is specified by a byte range and wherein each byte range includes audio data which is not used when playback is at the playback speed.
 12. A machine readable non-transitory storage medium storing executable instructions which, when executed, cause a data processing system to perform a method comprising: determining a set of parameters including a playback rate and a period of time that is available to download at least one I-frame; determining a first set of available I-frames, the I-frames in the first set being determined based on the set of parameters; determining a plurality of subsets of I-frames, each of the plurality of subsets of I-frames having a subset of the I-frames in the first set of available I-frames; determining an estimated download time for each of the plurality of subsets of I-frames; selecting one of the plurality of subsets of I-frames based upon the estimated download times and the set of parameters; receiving and displaying I-frames in the selected one of the plurality of subsets of I-frames.
 13. The medium as in claim 12 wherein the displaying of I-frames provides a trickplay playback mode, at the playback rate which is other than 1×, of video content in the I-frames and wherein each of the I-frames is retrieved using a tag, associated with a URL, that includes a byte range identifying a portion of a file containing the corresponding I-frame.
 14. The medium as in claim 13 wherein the set of parameters further includes a display deadline parameter and a current movie time of a current I-frame being displayed, and wherein the period of time is derived from the current movie time and the playback rate and the display deadline parameter.
 15. The medium as in claim 14 wherein the display deadline parameter is set as a fixed duration of time in a range of about ½ second to about 2 seconds and wherein the display deadline parameter is multiplied by the playback rate to produce a product, which is a time value, that is added to the current movie time to derive the period of time.
 16. The medium as in claim 15 wherein each of the plurality of subsets of I-frames has a predetermined cadence which differs among the plurality of subsets.
 17. The medium as in claim 16 wherein the number of I-frames in each of the plurality of subsets is limited by a predetermined maximum number.
 18. The medium as in claim 17 wherein the predetermined cadence of each of the plurality of subsets of I-frames is one of: (a) every one of the available I-frames in the first set; (b) every other one of the available I-frames; and (c) every third one of the available I-frames.
 19. A data processing system comprising: means for determining a set of parameters including a playback rate and a period of time that is available to download at least one I-frame; means for determining a first set of available I-frames, the I-frames in the first set being determined based on the set of parameters; means for determining a plurality of subsets of I-frames, each of the plurality of subsets of I-frames having a subset of the I-frames in the first set of available I-frames; means for determining an estimated download time for each of the plurality of subsets of I-frames; means for selecting one of the plurality of subsets of I-frames based upon the estimated download times and the set of parameters; means for receiving and displaying I-frames in the selected one of the plurality of subsets of I-frames.
 20. The system as in claim 19 wherein the displaying of I-frames provides a trickplay playback mode, at the playback rate which is other than 1×, of video content in the I-frames and wherein each of the I-frames is retrieved using tag, associated with a URL, that includes a byte range identifying a portion of a file containing the corresponding I-frame.
 21. The system as in claim 20 wherein the set of parameters further includes a display deadline parameter and a current movie time of a current I-frame being displayed, and wherein the period of time is derived from the current movie time and the playback rate and the display deadline parameter.
 22. The system as in claim 21 wherein the display deadline parameter is set as a fixed duration of time in a range of about ½ second to about 2 seconds and wherein the display deadline parameter is multiplied by the playback rate to produce a product, which is a time value, that is added to the current movie time to derive the period of time.
 23. The system as in claim 22 wherein each of the plurality of subsets of I-frames has a predetermined cadence which differs among the plurality of subsets.
 24. The system as in claim 23 wherein the number of I-frames in each of the plurality of subsets is limited by a predetermined maximum number.
 25. The system as in claim 24 wherein the predetermined cadence of each of the plurality of subsets of I-frames is one of: (a) every one of the available I-frames in the first set; (b) every other one of the available I-frames; and (c) every third one of the available I-frames. 